Organic Light-Emitting Diode (OLED) is a current-driven active light-emitting device, and has advantages of self illumination, rapid response, wide view angle, and capable of being manufactured on a flexible substrate, etc. It can be predicted that Organic light-emitting display based on OLEDs will be popular in the field of display. Each display unit of the organic light-emitting display includes an OLED, and the OLED can be divided into Passive Matrix Driving OLED (PMOLED) and Active Matrix Driving OLED (AMOLED) according to the manner in which OLED is driven. Active Matrix Driving OLED (AMOLED) is widely used in the display with large amount of information due to its high display quality. In AMOLED, for each OLED, a current flowing through the OLED is controlled by a Thin Film Transistor (TFT) circuit, and the OLED and the TFT circuit for driving the OLED constitute a pixel circuit. Therefore, in order to ensure evenness of the luminance of an Active Organic Light-Emitting display panel, it is necessary for the characteristics of TFTs located in different regions of a back board for driving OLEDs to be consistent.
A threshold voltage of a TFT depends on many factors including doping of a first electrode of the TFT, thickness of dielectric medium in the TFT, material of a gate of the TFT and excess charges in the dielectric medium in the TFT. At present, during the manufacturing process of a back board, particularly a back board with large size, it is difficult to achieve the consistence in such factors due to the limitation of the process condition and level, so that drifts in threshold voltages of respective TFTs are not consistent. In addition, the drifts in the threshold voltages of respective TFTs will be inconsistent due to the decrease of TFT stability caused by a long time operation. The variance of the drifts in the threshold voltages of respective TFTs then cause variance of the currents flowing through the respective TFTs, and thus the evenness of the luminance of OLEDs driven by these currents deteriorates.